312 The American Geologist. May. isos 
galls intrusive in the metamorpbic tuff's that contain, on Little 
(irizzly creek, fossils of Carboniferous age. 
Mr. J. S. Diller, in the text of the Lassen Peak sheet, states that 
' 'On the southwest slope of Chip creek the sedimentar}- rocks in 
contact with the diorite were greatl_y altered at the time of its 
eruption," showing the diorite to be the younger rock. The 
diorite referred to is the quartz-raica-diorite of the Spanish Peak 
area. Mr. Diller considers these sedimentar}" rocks, however, 
of Paleozoic age, and there is thus at present no evidence ex- 
tant that the granite of Plumas count}' is intruded into rocks 
later in age than the Carboniferous, but there is evidence that 
much of the granite of the Sierra Nevada further south is of 
Mesozoic age. 
Since the fall of 1885, Mr. Waldemar Liudgreu and myself 
have been engaged, under the authority of Mr. Gr. F. Becker, in 
studying the geology of the central Sierra Nevada. (3ver seven 
thousand square miles of the Gold Belt have been carefullj- map- 
ped, and the relations of the intrusive rocks, granite or grano- 
diorite, gabbro, diabase, et cetera, to the sedimentar}' rocks and 
to each other have been studied at many points. The results 
show that the granite is almost inv^ariably of j'ounger age than the 
associated sedimentary rocks. Much of it is later than the dia- 
base, which is placed by Mr. Mills in the Lower Mesozoic group. 
Thus to the southwest of Placerville (see Placerville geological 
atlas sheet) the granite has displaced the great diabase dike that 
lies just west of the Mother lode area of "Mariposa slates." 
In the southern Sierra Nevada, at Mineral King, there is a body 
of Triassic rocks containing fossils enclosed in the granite which, 
there forms the bulk of the range. As has been noted in the 
review of the paper on the Mother lode, the granite to the south of 
Mariposa is said by Fairbanks* to have cut off and metamorphosed 
the sedimentar}' series, including the Mesozoic Mariposa slates; 
and Mr. Lingreen found the Mariposa slates at Folsom to have 
been metamorphozed b}' the granite. It can then be stated with 
some confidence that much of the granite of the Sierra Nevada is 
post-Paleozoic in age. 
The lower Mesozoic group is characterized by large masses of 
greenstones, by which term Mr. Mills appears usually to mean 
rocks of the diabase series. In conglomerate in the Calaveras- 
*Tenth Ann. Rep. State Mineralogist, California, p. 3.5. 
